1. Field of the Invention
The present invention relates to a rotating force transmitting apparatus for transmitting a rotating force and an image forming apparatus such as a copying machine, a printer, a facsimile machine, and the like that is equipped with the rotating force transmitting apparatus and employs an electrophotographic process, an electrostatic recording process or the like.
2. Description of Related Art
The principal part of a full color electrostatic copying machine being an example of an image forming apparatus equipped with a rotating force transmitting apparatus will be described.
The full color electrostatic copying machine records an image having a plurality of colors on a recording medium by means of a digital image printer portion (hereinafter referred to as a xe2x80x9cprinter portionxe2x80x9d) on the basis of image information from a color image reader portion (hereinafter referred to as a xe2x80x9creader portionxe2x80x9d) for reading the image information on an original.
As shown in FIG. 5, in the printer portion, a pre-exposure lamp 11, a corona charger 2, a laser exposure optical system (not shown), a Y-developing unit 4y, a C-developing unit 4c, an M-developing unit 4m and a Bk-developing unit 4Bk being four developing devices for different colors, means 13 for detecting a quantity of light on the photosensitive drum 1, a transferring apparatus (not shown), a cleaning device 6 and the like are disposed around the photosensitive drum 1 being a latent image bearing member. The Y-developing unit 4y is a developing unit for yellow. The C-developing unit 4c is a developing unit for cyan. The M-developing unit 4m is a developing unit for magenta. The Bk-developing unit 4Bk is a developing unit for black.
When an image is formed by the printer portion, the charger 2 uniformly charges the photosensitive drum 1 after the photosensitive drum 1 has rotated in the direction indicated by the arrow to eliminate residual charges on the outer periphery of the photosensitive dram 1 with the pre-exposure lamp 11. Then, light images E are irradiated on the photosensitive drum 1 so that latent images of respective separated colors of the light images E are formed on the photosensitive drum 1.
Next, the latent images on the photosensitive drum 1 are developed by the operations of the developing units 4y, 4c, 4m and 4Bk corresponding to each separated color, and the images of toner being a powder developer having a base composed of a resin and a pigment are formed on the photosensitive drum 1. Incidentally, the developing units 4y, 4c, 4m and 4Bk are configured to approach the photosensitive drum 1 alternatively correspondingly to each separated color by the operations of respective eccentric cams 24y, 24c, 24m and 24Bk.
On the other hand, a recording material being a recording medium contained in a recording-material cassette (not shown) is fed to a transferring portion formed between the photosensitive drum 1 and the transferring apparatus (not shown) by the conveying system of the electrostatic copying machine, and the toner images on the photosensitive drum 1 are transferred on the recording material by the transferring apparatus. After that, the recording material on which the color image is formed is delivered to the outside.
The rotating force transmitting apparatus 100 for rotating each of the developing units 4y, 4c, 4m and 4Bk for each color will be described.
FIG. 6 is an expanded view of the rotating force transmitting apparatus 100. A rotating force from a drive motor (not shown) is transmitted to an input pulley 102, an input shaft 103 and a distributing gear 104 by a timing belt 101. The distributing gear 104 engages with an M-clutch gear 109m, a C-clutch gear 109c and idler gears 105 and 107. A rotating force from the idler gear 105 is transmitted to a Bk-clutch gear 109Bk through the idler gear 106, and a rotating force form the idler gear 107 is transmitted to a Y-clutch gear 109y through the idler gear 108.
Now, when an M-clutch 110m is turned on, the M-developing unit 4m is rotated through an output shaft 111m, an output gear 112m and a sleeve gear 113m. Similarly, when a C-clutch 110c is turned on, the C-developing unit 4c is rotated through an output shaft 111c, an output gear 112c and a sleeve gear 113c. When a Y-clutch 110y is turned on, the Y-developing unit 4y is rotated through an output shaft 111y, an output gear 112y and a sleeve gear 113y. When a Bk-clutch 110Bk is turned on, the Bk-developing unit 4Bk is rotated through an output shaft 111Bk, an output gear 112Bk and a sleeve gear 113Bk. A pair of supporting plates 114 and 115 supports the input shaft 103 and the output shafts 111m, 111c, 111y and 111Bk rotatably.
The operations of the pressure of each of the developing units 4y, 4c, 4m and 4Bk, clutching timing and the like will be described.
The operations will be described with reference to the timing charts of FIG. 7, FIG. 8 and FIG. 9. Hereupon, concrete numerical values are set for making the descriptions of the operations easy to understand. Incidentally, the numerical values are for the sake of reference, and the related art is not restricted to the numerical values.
The diameter of the photosensitive drum 1 is set at 180 mm, and the peripheral speed (or the image-forming process speed) of the photosensitive drum 1 is set at 200 mm/sec. The developing units 4y, 4c, 4m and 4Bk are disposed around the photosensitive drum 1 within an angular range of 0 degrees to 100 degrees with respect to a horizontal direction in the clockwise direction equidistantly (at the interval of 33.3 degrees) in the order of yellow (Y), cyan (C), magenta (M) and black (Bk). The order of developing is M, C, Y and Bk.
A case where an image of the A-4 size is continuously copied in a full color copying mode will be described.
Abscissa axes of the timing charts shown in FIG. 7 to FIG. 9 indicate time (or distance). FIG. 9 is an enlarged view of the M-developing operation shown in FIG. 7 and FIG. 8. The waveforms in the top row to the third row in FIGS. 7 and 8 indicate latent images on the photosensitive drum 1 at the M-developing position, the pressuring operation of the M-developing unit 4m to the latent images, and the on-off actions of the M-clutch 110m, respectively. Because the latent images for two prints are formed on the photosensitive drum 1 during the rotation of the photosensitive drum 1 in the A-4 continuous copying mode, a reference mark M1 designates a latent image of magenta in the copy on the first sheet, and a reference mark M2 designates a latent image of magenta in the copy on the second sheet.
Similarly, the waveforms in the fourth row to the sixth row in FIG. 7 indicate latent images on the photosensitive drum 1 at the C-developing position, the pressuring operation of the C-developing unit 4c, and the actions of the C-clutch 110c, respectively. The waveforms in the seventh row to the ninth row in FIG. 7 indicate latent images on the photosensitive drum 1 at the Y-developing position, the pressuring operation of the Y-developing unit 4y, and the actions of the Y-clutch 110y, respectively. The waveforms in the tenth row to the twelfth row in FIG. 7 indicate latent images on the photosensitive drum 1 at the Bk-developing position, the pressuring operation of the Bk-developing unit 4Bk, and the actions of the Bk-clutch 110Bk, respectively.
The formation of the latent images is started. The latent image of each color is equidistantly formed on the outer periphery of the photosensitive drum 1 having the diameter of 180 mm for two prints of the A-4 size. Because the length of the outer periphery of the photosensitive drum 1 is about 565.2 mm and the width of the A-4 size is 210 mm, the interval of the latent images is 72.6 mm from the calculation of: (565.2xe2x88x92210xc3x972)÷2=72.6 mm. The time of the interval of the latent images is 0.363 second from the calculation of: 72.6 (mm)÷200 (mm/second)=0.363 second.
The pressurization of the M-developing unit 4m to the photosensitive drum 1 is begun before 0.25 second short of (before 50 mm short of a position at) a point of time when the leading edge of the latent image M1 reaches the M-developing position. After 0.05 second (behind 10 mm) from the beginning of the pressure-contact of the M-developing unit 4m with the photosensitive drum 1, the M-clutch 110m is turned on as shown in FIG. 9. After 0.05 second (behind 10 mm) from the turning on of the M-clutch 10m, the peripheral speed of the M-developing unit 4m reaches a predetermined speed.
The development sleeve of the M-developing unit 4m is required to rotate at the predetermined peripheral speed before the completion of the pressure-contact of the development sleeve to the photosensitive drum 1. When the development sleeve does not rotate at the predetermined peripheral speed at the time of the pressure-contact thereof, there is a case where images are disturbed owing to the generation of xe2x80x9cadherent foggingxe2x80x9d being a phenomenon such that unnecessary toner adheres on the photosensitive drum 1.
After 0.15 second, or behind 30 mm, from the beginning of the pressure-contact of the M-developing unit 4m to the photosensitive drum 1, the pressure-contact of the M-developing unit 4m to the photosensitive drum 1 is completed. At this time, the development sleeve of the M-developing unit 4m rotates at the predetermined peripheral speed as described above.
Moreover, the M-developing unit 4m completes the pressure-contact to the photosensitive drum 1 with a clearance of the time of 0.1 second, or the distance of 20 mm, before the leading edge of the latent image M1. Then, the latent images M1 and M2 are developed.
After 0.1 second (behind 20 mm) from the completion of the development of the latent image M2, the M-developing unit 4m begins to separate from the photosensitive drum 1. The development sleeve of the M-developing unit 4m is also required to rotate at the predetermined peripheral speed when the M-developing unit 4m separates from the photosensitive drum 1 similarly at the time of the pressure-contact thereof. When the development sleeve is not rotating at the predetermined peripheral speed, the xe2x80x9cfoggingxe2x80x9d is generated. In this case, when the M-developing unit 4m separates from the photosensitive drum 1, the M-clutch 110m is in a turned-on state thereof. Consequently, the xe2x80x9cfoggingxe2x80x9d is not generated. After 0.05 second (behind 10 mm) from the beginning of the separation of the M-developing unit 4m, the M-clutch 110m turns off.
After 0.05 second (behind 10 mm) from the turning off of the M-clutch 110m, the M-developing unit 4m completely stops.
After 0.15 second (behind 30 mm) from the beginning of the separation operation of the M-developing unit 4m, the separation operation thereof is completed. The separation operation should be completed before the arrival of the next latent image C1 at the M-developing position. When the separation operation is not completed at the time of the arrival of the next latent image C1, there is the possibility that the latent image C1 of cyan is developed by the M-developing unit 4m. 
In this example, the separation is completed with a clearance of the time of 0.113 second (a clearance of the distance of 22.6 mm) before the leading edge of the latent image C1 of cyan.
Next, the operation of the C-developing unit 4c will be described.
The C-developing unit 4c is disposed upstream of the M-developing unit 4m by the 33.3 degrees in the rotational direction of the photosensitive drum 1. Consequently, a latent image on the photosensitive drum 1 arrives at the C-developing position earlier than the arrival thereof at the M-developing position by the distance of: 180xc3x97xcfx80xc3x97(33÷360)=51.81 mm≈52 mm, namely by the time of: 51.81÷200=0.259 second≈0.26 second. Because the timing charts shown in FIG. 7 and FIG. 8 are drawn by the use of the same time axes, the latent images at the C-developing position are shifted to the left side in the timing chart of FIG. 7 by the 0.26 second (by the 52 mm).
The operation of the C-developing unit 4c is similar to that of the M-developing unit 4m. 
After 0.113 second (behind 22.6 mm) from the passing through of the trailing edge of the latent image M2 at the C-developing position, the pressure-contact of the C-developing unit 4c to the photosensitive drum 1 is begun. After 0.05 second (behind 10 mm) from the beginning of the pressure-contact of the C-developing unit 4c to the photosensitive drum 1, the C-clutch 110c turns on.
After 0.05 second (behind 10 mm) from the turning on of the C-clutch 110c, the peripheral speed of the C-developing unit 4c reaches the predetermined peripheral speed. After 0.15 second (behind 30 mm) from the beginning of the pressure-contact of the C-developing unit 4c to the photosensitive drum 1, the pressure-contact of the C-developing unit 4c to the photosensitive drum 1 is completed. At this time, the C-developing unit 4c has reached the predetermined peripheral speed, and the pressure-contact of the C-developing unit 4c is completed with a clearance of the time of 0.1 second (the clearance of the distance of 20 mm) before the leading edge of the latent image C1. Then the latent image C1 and a latent image C2 are developed.
After 0.1 second (behind 20 mm) from the completion of the development of the latent image C2, the C-developing unit 4c begins to separate from the photosensitive drum 1.
After 0.05 second (behind 10 mm) from the beginning of the separation of the C-developing unit 4c, the C-clutch 110c turns off. After 0.05 second (behind 10 mm) from the turning off of the C-clutch 110c, the C-developing unit 4c completely stops.
After 0.15 second (behind 30 mm) from the beginning of the separation operation of the C-developing unit 4c, the C-developing unit 4c completes its separation operation. At this time, the separation of the C-developing unit 4c is completed with a clearance of the time of 0.113 second (a clearance of the distance of 22.6 mm) to the leading edge of the following latent image Y1.
Similarly, the Y-developing unit 4y is disposed upstream of the C-developing unit 4c by the 33.3 degrees in the rotational direction of the photosensitive drum 1. Consequently, latent images at the Y-developing position are shifted to the left side in the timing chart of FIG. 7 by the 0.261 second (by the 52 mm).
The operation of the Y-developing unit 4y is similar to those of the M-developing unit 4m and the C-developing unit 4c. 
Moreover, the Bk-developing unit 4Bk is disposed downstream of the Y-developing unit 4y by the 100 degrees in the rotational direction of the photosensitive drum 1. Consequently, latent images at the Bk-developing position are shifted to the right side in the timing chart of FIG. 8 by the amount of: 180xc3x97xcfx80xc3x97(100÷360)=157 mm, or the amount of: 157÷200=0.785 second.
The operation of the Bk-developing unit 4Bk is similar to those of the M-developing unit 4m, the C-developing unit 4c and the Y-developing unit 4y. Moreover, because the M-developing unit 4m is disposed upstream of the Bk-developing unit 4Bk by the 33 degrees in the rotational direction of the photosensitive drum 1, the latent images at the M-developing position are shifted to the left side by the 0.261 second (by the 52 mm) in the timing chart of FIG. 8 with respect to the latent images at the Bk-developing position.
After that, the aforesaid operations are repeated with keeping the aforesaid relations.
However, the following disadvantages have been produced in the aforesaid related art configuration at some timing between the transmission of the driving of each of the developing units 4y, 4c, 4m and 4Bk.
Although the operation of each of the developing units 4y, 4c, 4m and 4Bk is performed as described above, the relations between each of the developing units 4y, 4c, 4m and 4Bk are now noticed. The timing of the turning on of the C-clutch 110c will be described. Immediately before the turning on of the C-clutch 110c, the M-developing unit 4m is in a state of pressure-contact, and the M-clutch 110m is in its turned-on state and the latent image M2 is being developed. FIG. 6 is referred while the following description is made. Driving from a drive motor (not shown) is transmitted to the timing belt 101, the input pulley 102, the input shaft 103, the distributing gear 104, the M-clutch gear 109m, the M-clutch 110m, the output shaft 111m, the output gear 112m and the sleeve gear 113m in the order, and thereby the drive motor drives the M-developing unit 4m to rotate it. In such a state, when the C-clutch 110c is turned on, the driving from the distributing gear 104 is transmitted to the C-clutch gear 109c, the C-clutch 110c, the output shaft 111c, the output gear 112c, and the sleeve gear 113c in the order. Then, the driving is to drive the C-developing unit 4c to rotate it.
At this time, the load and the inertia of the C-developing unit 4c are transmitted to the distributing gear 104 through the reverse path of the path at the time of the transmission of driving, and the transmitted load and the transmitted inertia instantaneously lowers the rotational speed of the distributing gear 104.
The lowering of the rotational speed of the distributing gear 104 is transmitted to the M-clutch gear 109m, the M-clutch 110m, the output shaft 111m, the output gear 112m and the sleeve gear 113m in the order. Finally, the speed of the M-developing unit 4m is lowered.
The M-developing unit 4m is developing the position thereof before 0.098 second (before 19.6 mm) from the trailing edge of the latent image M2 at this time. Consequently, when the rotational speed of the development sleeve of the M-developing unit 4m is lowered, the feeding of toner to the latent image M2 becomes uneven, and unevenness in a shape of lateral strips are produced at the corresponding positions on an image.
These disadvantages are not limited to the relations between the M-developing unit 4m and the C-developing unit 4c, and they are generated in any timing of the transmission of driving to one developing unit during the developing of a latent image by another developing unit.
In the C-developing unit 4c, the lowering of the rotational speed during the development of the trailing edge of the latent image C2 owing to the turn on of the Y-clutch 110y is produced at a time designated by a reference numeral (i) in FIG. 7 to generate lateral stripes. In the Bk-developing unit 4Bk, the lowering of the rotational speed during the development of the trailing edge of the latent image Bk2 owing to the turn on of the M-clutch 110m is produced at a time designated by a reference numeral (ii) in FIG. 8 to generate lateral stripes.
Because the developing positions of the Y-developing unit 4y and the Bk-developing unit 4Bk are sufficiently distant and there is no timing when two color clutches of the Y-clutch 110y and the Bk-clutch 110Bk are in their turned-on states at the same time between the Y-developing unit 4y and the Bk-developing unit 4Bk, no disadvantage such that the lateral stripes are produced is presented.
Accordingly, it is considerable that the diameter of the photosensitive drum 1 is enlarged to widen the intervals between latent images so that the lateral stripes are not produced. However, in this case, another problem such that the shape of the apparatus becomes large is presented.
Moreover, it is also considerable to thin out the rotations of the photosensitive drum 1 by a half rotation thereof to form the next latent image C1 after the formation of the latent images M1 and M2 (i.e. the latent image C1 in the related art is not formed, and the latent image C1 is formed at the position of the latent image C2 in the related art and the latent image C2 is formed at the position of the latent image Y1 in the related art). However, in this case, another problem such that the printing speed thereof decreases to the ⅔ of that of the related art is presented.
A method for performing the pressurization operation in the developing process and the clutch operations at high speeds would increase the shocks at the time of the pressurization to disturb the formation of latent images, and thereby image blurring would be caused. Besides, the necessity of the changes of the clutches 110m, 110c, 110y and 110Bk to be ones having a large capacity would be brought about, which would make the cost of the apparatus increase largely.
Anyway, for the escape of these disadvantages, it is necessary to employ a structure not to perform the transmission of driving to a developing unit while another developing unit is developing a latent image.
One object of the present invention is to provide a rotating force transmitting apparatus capable of preventing the occurrence of a phenomenon such that, when the rotation of one of a first and a second rotary members is begun while the other of them is rotating, the rotational speed of the rotating rotary member is decreased.
Another object of the present invention is to provide an image forming apparatus capable of preventing the occurrence of the phenomenon such that, when the rotation of one of the first and the second rotary members is begun while the other of them is rotating, the rotational speed of the rotating rotary member is decreased.
A further object of the present invention is to provide an image forming apparatus capable of preventing a faulty image owing to the decrease of the rotational speed of a development rotary member to obtain a high quality image at a high printing speed without enlarging the shape of the apparatus and increasing the cost thereof.
The other objects, features and advantages of the present invention will become more apparent from the following description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings.